A 4th Generation (4G) communication system is expected to be commercialized around 2010. Research is being conducted to provide a service with a data transfer rate of 1 Gigabit per second (Gbps) when stationary and a data transfer rate of at least 100 Megabit per second (Mbps) when on the move. Many new technologies and evolved 2G/3G technologies are being evaluated as candidates for the proposed 4G communication system. Although these technologies provide voice call services as well as high-speed data services based on different service concepts, there is still no breakthrough technology which can be called a 4G technology. According to the existing papers and documents, the 4G technology candidates can be classified into the following three groups.
The first group includes a Wideband Code Division Multiple Access (WCDMA) service and a High-Speed Downlink Packet Access (HSDPA) service, which are evolved from existing 2G or 3G cellular networks and which have been provided by the 3G Partnership Project (3GPP), and also includes a Code Division Multiple Access 2000 (CDMA2000) service, a 1x Evolution for Data Only (1xEVDO) service, and a 1x Evolution for Data and Voice (1xEVDV) service, which have been provided by a 3G Partnership Project 2 (3GPP2). These technologies provide an average data transfer rate of only several Mbps. Advantageously, however, the technologies can support a seamless call or data service even when moving at a high-speed and can provide service in almost all areas due to wide cell coverage.
The second group includes a Wireless Metropolitan Area Network (WMAN) service, which is scheduled to be provided as a metropolitan data service by the American Institute of Electrical Electronics Engineers (IEEE) 802.16 protocol. WMAN service is also referred to as IEEE 802.16 service. The WMAN corresponds to WiBro, which was standardized in 2005 by the Republic of Korea. Further, the WMAN is called WiMax in the United States where Intel dominates the market. The WMAN is similar in concept to a conventional cellular network, but can support an average data transfer rate of up to several tens of Mbps. The WMAN was originally designed to support medium-speed mobility up to 60 km/h in a metropolitan area where many people gather and provides cell coverage of up to 1 km.
The third group includes Wireless Local Area Network (WLAN) service, which was developed under IEEE 802.11 so as to replace the existing wired Internet service. The WLAN was standardized in 1999, and has evolved through IEEE 802.11a/b to IEEE 802.11g. The WLAN is now in commercial use and is constantly evolving. At present, the WLAN provides an average data transfer rate of several tens of Mbps, but is expected to provide an average data rate of up to several hundreds of Mbps in the near future. The WLAN is expected to be the first of the 4G technology candidates that can implement a data transfer rate of 1 Gbps when stationary. Disadvantageously, however, the WLAN hardly supports mobility, and thus communication can be provided only within a local cell coverage area of up to 100 meters.
Another candidate for the 4G technologies is an IEEE 802.15 service called “Wireless Personal Area Network (WPAN) service”. Although similar to the WLAN, the WPAN provides a much smaller cell coverage than the WLAN and supports data communication with a data transfer rate of at least 1 Gbps. For example, the WPAN service is implemented using ultra near-field high-speed communication technologies such as Ultra-Wideband (UWB) technology and Bluetooth technology. Hereinafter, WLAN and WPAN will be collectively referred to as “WLAN”.
FIG. 1 illustrates a radio access environment in which a plurality of heterogeneous networks is used.
A network 111 having the largest cell coverage indicates a 2G/3G cellular network. A network 112 having a medium-sized cell coverage indicates a WMAN. A network 113 having the smallest cell coverage indicates a WLAN. It will be assumed that a terminal 103 can use all of the aforementioned network services.
The terminal 103 can connect and communicate with the cellular network in an area 101. The terminal 103 can connect and communicate with the cellular network or the WMAN in an area 102. The terminal 103 can connect and communicate with the cellular network, the WMAN, and the WLAN in an area 103. As such, when the terminal 103 can connect with several wireless communication networks, according to the conventional technologies, the terminal 103 performs a switching operation through either a vertical handover or radio reconfiguration to select only one of the network services providing the best throughput.
However, when one of the network services is selected, the following problems may occur.
First, when a terminal moves with a certain speed, a handover occurs frequently. Thus, control information is frequently exchanged between different wireless systems, which may lead to an overhead against high-speed data transmission.
Second, when a terminal connected to a WLAN or WMAN moves with a high speed that cannot be supported in the WLAN or WMAN, communication may be broken since data transmission and reception cannot be smoothly made. If communication is broken, the terminal reconnects to a cellular network that can support a high-speed data service, which may lead to another overhead.